1. Field of the Invention
The present invention relates to a dental cutting tool holder for detachably installing a dental cutting tool which is used for cutting hard tissues including teeth, dentary, etc., in the head of a handpiece.
2. Description of the Related Art
Indispensable for dental care are cutting operations for teeth aiming at preparing cavities, forming abutment teeth, cutting off carious sites, enlarging root canals, etc., and instruments used for such cutting operations include, for example, air turbine handpieces. This type of cutting tool is detachably installed in the head of a handpiece and driven for rotation at a high speed on the order of 400-500 thousand rpm. Therefore, in order to prevent the dislocation of the cutting tool in the oral cavity of the patient under care, it is necessary that the cutting tool be securely held in the head of the handpiece. In addition, since a variety of types of cutting tools are used appropriately depending on the shape of the cavity, the cutting site, etc., preferably they are installed in the head of a handpiece in a readily detachable manner.
Representative of the prior art is, for example, the one described in Japanese Unexamined Utility Model Publication JP-U 60-27908 (Japanese Examined Utility Model Publication JP-Y2 61-30650). According to this device of the prior art, a chuck member, a counterpart of the collet chuck according to the present invention, in the head for receiving a cutting tool is provided with a plurality of chuck bits, and when the chuck member is displaced in one axial direction upon insertion of the cutting tool, the chuck member is pressed against the tapered inner circumference of the inserted spindle while the outer circumferences of the chuck bits are pressed inward in a radial direction, thereby providing a structure which allows the inner circumferences of the inward displaced chuck bits to press against the outer circumference of the cutting tool to hold the cutting tool.
This device of the prior art, however, produces ununiform pressure from the respective chuck members on the cutting tool because of the dimensional variabilities of the respective chuck bits due to discrete structures of the chuck bits and the chuck member. Consequently, the axis of the spindle does not match the axis of the cutting tool, resulting in creation of vibrations during cutting which may cause the patient pain while cutting the tooth. Furthermore, since the vibrations make a noise which tends to provoke fear and anxiety in patients, there is presented a problem of increased emotional upset.
Another embodiment of the prior art is described in, for example, Japanese Examined Utility Model Publication JP-U 3-53215. According to this prior art, there is formed a notched stepped section on the inner circumference of collet, corresponding to the collet chuck according to the present invention, in order to provide a structure which allows the corner section of the notched stepped section to engage in the outer circumference of the cutting tool by the chucking action, thereby preventing the cutting tool from being dislocated, even if force is exerted on the inserted cutting tool to facilitate its dislocation.
This device of the prior art, however, has a drawback in that even with great axial frictional force of the notched stepped section exerted on the cutting tool, the cutting tool slides in the direction of rotation during cutting due to extremely poor frictional force in the direction of rotation, eventually allowing the cutting tool to readily work down in spite of great clamping force applied on the cutting tool.
A further prior art is disclosed in, e.g., Japanese Unexamined Patent Publication JP-U 56-151035. This device of the prior art provides, as is shown in FIG. 15, a structure with a manipulation member 221 comprising a press cap with a recess 222 in the center. The inner bottom surface 223 of the recess 222 is plane, and due to the small contact area of the press cap and the finger, the finger must press harder. A much greater force must be applied in cases where the size of the finger does not fit the size of the recess 222. This additional requirement results in a heavy burden imposed on dentists who treat many patients daily, because the manipulation member must be used several times for each patient to change dental cutting tools.